1. Field of the Invention
The present invention relates generally to a shoe sole, and more particularly, to a shock absorbing device for the shoe sole.
2. Description of the Prior Art
A shoe sole needs cushioning or shock absorbing properties.
The conventional shoe sole typically dissipates and absorbs energy of landing shock, i.e., shock from the foot upon walking through compressive transformation of a shock absorbing device such as a midsole. However, such an energy absorption (loss) relying on only the compressive transformation will not ensure sufficient shock absorbing abilities due to its small amount of energy absorption in general.
On the contrary, increased thickness of the midsole to increase the energy loss may impair shoe sole""s lightweight properties and stability.
U.S. Pat. No. 4,798,010 discloses a shock absorbing device as depicted in FIG. 19(a).
In this prior art, a midsole 102 is interposed between an outsole 100 and an upper 101. The midsole 102 consists of a flexible elastic member (30 to 50 degrees in hardness) 103 and a rigid elastic member (60 to 80 degrees in hardness) 104 which are joined together via a joint surface 105. The joint surface 105 is corrugated.
Japan Utility Model Laid-open Pub. No. Hei6-17504 discloses a shock absorbing device as depicted in FIG. 19(b).
In this prior art, the midsole 102 is fitted with a shock absorbing device 106 having a corrugated section.
In these prior arts, loads from above bring about compressive transformations of the corrugated portions. However, such compressive transformations do not ensure by themselves sufficient shock absorbing properties.
U.S. Pat. No. 5,915,819 discloses a shock absorbing device as depicted in FIGS. 20(a) and 20(b).
In this prior art, a multiplicity of compressible chambers 202 are formed between a lower sheet-like member 200 and an upper sheet-like member 201. When a weight 203 is applied from above to the sheet-like member 201, the chambers 202 are put in compression, which compression provides a shock absorbing feature.
In this prior art, the upper and lower sheet-like members 200 and 201 are brought into pressure contact with each other at inclined faces 204, causing a slight shearing transformation. The upper and lower members 200 and 201 however involve a multiplicity of sharp edge and shoulder portions (differentiation-impossible points) 205 at which the sectional contour sharply varies. This impairs the continuity of transformation and hence suppresses the energy absorption attributable to the shearing transformation.
Additionally, due to formation of recessed portions 206 in the lower member 200, when the two members 200 and 201 come into pressure contact with each other at the inclined faces 204 as depicted in FIG. 20(b), the lower member 200 can deform such that convexed portions 207 of the lower member 200 migrate into the recessed portions 206 reducing support for inclined face 204. This reduces the contact pressure on the inclined faces 204 and impairs the energy absorption abilities attributable to the shearing transformation.
It is therefore an object of the present invention to provide a novel structure of a shock absorbing device for a shoe sole so as to facilitate the occurrence of a shearing transformation to thereby achieve an improvement in the shock absorbing properties.
In one aspect of the present invention to attain the above object, a shock absorbing device for a shoe sole comprises a lower layer having an upper face and an upper layer having a lower face.
The two layers are both made of an elastomer.
The upper face of the lower layer and the lower face of the upper layer are each formed to have substantially a corrugated section. (Hereinafter referred to the faces formed to have substantially the corrugated section as xe2x80x9ccorrugated facesxe2x80x9d).
The corrugated faces each have a plurality of top portions, a plurality of bottom portions, and a plurality of inclined portions joining the top portions and bottom portions, with the corrugated faces each being formed from essentially a smooth and continuous curvilinear surface.
The corrugated upper face and lower face mate with each other.
The two faces mated with each other (two mating faces) are in contact with each other at the inclined portions of the faces.
The two mating faces are spaced apart from each other at the top portions and/or at the bottom portions, with gaps being formed at the spaced-apart portions.
In another aspect of the present invention, a shock absorbing device for a shoe sole comprises a lower layer having an upper face and an upper layer having a lower face.
The two layers are both made of an elastomer.
The upper face of the lower layer and the lower face of the upper layer are each formed to have substantially a corrugated section.
The corrugated faces each have a plurality of top portions, a plurality of bottom portions, and a plurality of inclined portions joining the top portions and bottom portions.
The top portions of the upper face of the lower layer are formed with essentially a recess-free, upwardly convexed surface, the bottom portions of the lower face of the upper layer are formed with essentially a recess-free, downwardly convexed surface.
The corrugated upper face and lower face mate with each other.
The two mating faces are in contact with each other at the inclined portions of the faces.
The two mating faces are spaced apart from each other at the top portions and/or at the bottom portions, with gaps being formed at the spaced-apart portions.
In a further aspect of the present invention, a shock absorbing device for a shoe sole comprises a lower layer having an upper face, an upper layer having a lower face, and an intermediate layer interposed between the lower layer and the upper layer.
The upper face of the lower layer and the lower face of the upper layer are each formed to have substantially a corrugated section.
The corrugated faces each have a plurality of top portions, a plurality of bottom portions, and a plurality of inclined portions joining the top portions and bottom portions.
The corrugated upper face and lower face mate via the intermediate layer with each other.
The two mating faces are in contact via the intermediate layer with each other at the respective inclined portions.
The two mating faces are spaced apart from each other at the top portions and/or at the bottom portions, with gaps being formed at the spaced-apart portions.
According to the present invention, between the upper and lower layers having corrugated sections, gaps are formed at the top portions and/or at the bottom portions of the corrugations. Thus the application of loads from above causes a shearing transformation at the inclined portions in contact with each other, the shearing transformation arising from shearing of textures of the inclined portions along the inclined surfaces. Thus, the loads from above presents not merely the compressive transformation but also a shearing transformation which contributes to an improvement of the shock absorbing properties.
In the present invention, the corrugated faces are each formed from essentially a smooth and continuous curvilinear surface so that there exist no sharply varying points in the sectional contours, whereupon there will occur a shearing transformation not merely at the textures of the inclined portions but also at the top portions and bottom portions without impairing the continuity in the shearing transformation. Remarkably improved shock absorbing properties are thus achieved.
As used herein, xe2x80x9cthe corrugated faces are each formed from essentially a smooth and continuous curvilinear surfacexe2x80x9d means that the sectional contours include a contour consisting of a curve and a curve which are smoothly joined together and a contour consisting of a curve and a straight line which are smoothly joined together and that there exist a plurality of crests and troughs having no sharply varying points which make the differentiation thereat difficult.
In the present invention, on the other hand, the top portions of the upper face of the lower layer are formed with essentially a recess-free upwardly convexed surface, and the bottom portions of the lower face of the upper layer are formed with essentially a recess-free downwardly convexed surface. Thus, when the upper layer and the lower layer come into direct or indirect pressure contact with each other, the textures do not migrate into the top portions or bottom portions forming the convexed surfaces, thus adding to the contact pressure on the inclined portions. This results in an increased energy absorption capability attributable to the shearing transformation.
As used herein, xe2x80x9cessentially a recess-freexe2x80x9d means that there exist a plurality of top portions of upper face and bottom portions of lower face which are not recessed.
In the present invention, it is preferred that at least four crests and troughs mating each other are arranged in lattice points of a substantially plane lattice in the upper layer and the lower layer. Upon walking or running, the foot tends to land from lateral side to medial side and from rear to front, downward from diagonally above. In this manner, the landing shock has a directionality, and since the direction varies depending on the weight shifting after landing (the foot lands at the rear lateral side of the heel portion and thereafter the trajectory of the center of gravity varies as a function of the weight shifting), the arrangement of the crests and troughs in lattice points of a substantially plane lattice enables the shock that occurs upon landing to be relieved.
Furthermore, by virtue of the mutual separations of the two corrugated faces at their top portions and bottom portions, the upper layer and the lower layer textures can migrate diagonally downward, facilitating the shearing transformation, which contributes to a further improved cushioning.